dave o'leary <oleary@noc.sura.net> (09/24/90)
stox@balr.com (Ken Stox) writes: X-Telecom-Digest: Volume 10, Issue 671, Message 6 of 12 >Recently, we have been seeing a bit of discussion of the cost (to the >operating company) of a data call versus a voice call. All the >statements I have seen, so far, seem to agree that a data call costs >the operating company the same as a voice call. TTBOMK (To The Best Of >My Knowledge), this is not true for the following reasons: > First of all, I should state this is the case for a DIGITAL >phone system. If everything were still analog, many would be false. In >fact, this is where the problem lies! It seems that everyone is using >the analog case. > 1) Although your connection is analog in nature, it will only >be that way until it reaches the C.O. To the best of My knowledge, your connection is indeed analog to the CO in the general case, however.... > 2) Once digitized at the C.O., the digital data from your >phone call is blocked into packets of data which are routed through >the phone network. If the CO's are packetizing and integrating data and voice through the public network in the general case then I'd really like to hear about the details. These techniques will probably be common in the future (this is what ATM switching is all about) but I think there are only a couple of beta tests going on. > 3) Human speech contains a great deal of dead air/silence. >When you are pausing in a word/sentence/etc., you are no longer >sending data. The phone company can now send more packets of data over >that trunk line while you are pausing between word/sentences/etc. Byte interleaved multiplexing is done after the digitization - each analog signal gets a 64kb slot, times 24 slots plus framing bits yields the 1.544 Mb/s of a T1 line. Four T1's multiplexes to a T2, Seven T2's multiplex to a T3 (44.something Mb/s - this is how the signal generally travels over the inter-CO fiber and to the IXC POPs.) A modem's analog signal digitizes to the 64kb DS0 channel, just like a voice digitizes to a 64 kb DS0 channel. Sometimes compression is performed on the signals after digitization so more circuits can use a single DS0, I don't know how common this is, but the techniques are multiplexing rather than packet switching. > 4) Modems don't pause, they will use every available packet >for that data path. In other words, a modem conversation will not >allow any other packets through. The bits (either digitized voice or digitized data) are sent through the network in a 64kb virtual circuit. This 64kb is allocated for that particular call for the length of the call - nobody else's bits, either data or voice, are packet switched onto the virtual circuit. > So, we can now understand why the RBOC's get so blustered >about data traffic. The service that they expected you to use 50% of, >you are using 100% of. I am sure we all feel a great deal of pity for >that poor accountant, who, at this very moment is writhing in agony >over uncollected potential revenue. No doubt, in the not so distant >future, the RBOC's will figure out how to bill you on a packet by >packet basis. This may be the beginning of a much more equitable >method of billing ( right, when hell freezes over :-> ) by which the >customer purchases X number of packets at a given routing grade. Well, >someday, maybe ISDN. Well, there are a slew of acronyms for technologies and services that if/when they are implemented or available all the stuff typed in above will change. ATM, "Fast Packet", SMDS, Frame Relay, BISDN ... etc. Lots of fun. Of course, what Ken said earlier in his message about a digital network and integrated voice and data packetizing may apply to a private network. If such private networks do exist in practice, I'd be interested in hearing about them. From what I understand, however, the situation described does not exist in the present public network. dave o'leary oleary@noc.sura.net SURAnet NOC Mgr. (301)982-3214